This contract has as its goals the following: 1) to estimate of rate of transmission of HIV infection from infected mother to child, to examine cofactors which may facilitate this transmission, to describe the impact of HIV infection on the outcome of pregnancy (both obstetric and pediatric), and to describe the natural history of HIV infection in children who have vertically transmitted disease. 2) to describe the neurologic and neurodevelopmental impact of HIV infection on children with infection acquired as a result of maternal fetal transmission. This study is being conducted as a prospective, longitudinal follow-up cohort study in 3 centers in New York City. Pregnant women at risk for HIV infection are enrolled, with the infected women serving as index cases and the uninfected, at-risk women as the comparison group. The women are followed throughout pregnancy, and delivery and for four years post-partum together with their children.